Building a fence in a particular area of farmland to prevent the invasion of animals, particularly wild animals has been widely used for a long time. Furthermore, in certain cases, an electric current of high voltage is allowed to flow in this fence to give electrical shock to wild animals when contacted with the fence in order to keep away the wild animals. However, unintentional electrical shock may be delivered to humans or livestock or pet animals, not wild animals, when contacted with the fence, which is a disadvantage of electric fences.
Patent Literature 1 (U.S. Pat. No. 7,081,821) discloses an electronic fence system and controlling method thereof, in which a fence wire is buried in the ground along a boundary of a confined area restricting an activity area of an animal to radiate a boundary defining radio signal over the air, and when the animal worn with a receiver including stimulation applying means accesses the boundary of the confined area, the receiver receives the boundary defining radio signal of the fence wire and applies stimulation to the animal. Meanwhile, in the system of Patent Literature 1, a mode selection signal for selecting a mode in which stimulation is applied to the animal (a mode in which only electrical shock is applied and a mode in which vibration is applied first and electrical shock follows it) is embedded in the radio signal, and the receiver detects the radio signal and applies stimulation in a mode depending on the mode selection signal embedded in the radio signal.
However, conventional animal containment systems including Patent Literature 1 are basically designed to control only one animal. Of course, the system of Patent Literature 1 may control a plurality of animals using one transmitter (fence wire) if a plurality of animals is worn with each receiver for one transmitter (fence wire). However, in this case, because the radio signal radiated through the fence wire is common to all the receivers, stimulation of the same intensity or the same mode is applied to the plurality of animals which is trained at different levels or has different sensitivities to stimulation.
To solve this problem, for example, optimal stimulation can be applied to each animal by embedding signals of different intensities or different mode selection signals for each of the plurality of animals through time-division modulation of the radio signal. However, in this case, modulation of the radio signal is complex, and when many animals go over the boundary of the confined area very quickly at a point in time, dealing with it is difficult.